This means that ground is shared between left and right channel.
These 3-pin plugs, so called TRS (tip-ring-sleeve) plugs, have contact for left channel, right channel, and ground. In headphones these two circuits are the left and right speaker.īasically all headphones are connected to source using 3.5 mm or 6.3 mm plug. What is common-impedance coupling?Ĭommon-impedance coupling occurs when two or more circuits share the same return current path, ground path. Therefore, I want to point out another benefit of balanced interconnection with headphones: reduced common-impedance coupling. While noise and interference suppression is very important especially in higher-impedance and/or higher-speed signals, in low-impedance headphone connections it is not crucial. See references at the end of the post for more detailed explanation. This common-mode signal is then heavily attenuated at the next stage where only differential signal is amplified. Interference that gets through the shield is picked both by hot and cold lead, and as the impedance to ground is equal the interference generates equal voltage on both leads. Shield is like an enclosure, it is not part of the signal path now so most of the external interference never gets to the signal leads inside the shield. This is achieved due to separate shield (if used) and balanced impedance. Typically balanced (line-level) interconnections are used because of their good noise suppression. What are the benefits of balanced interconnection? Higher signal level can be achieved and some performance figures may be slightly better but I do not see big advantages if modern ICs are used anyway. There is of course nothing wrong to do it like this, it just means increased cost and complexity as part of the output stage must be doubled. In practice there are of course impedances in cables and connectors but the point is that the relative difference between these paths is significant.Īnother disadvantage is that all noise and interference that gets through the shield becomes part of the signal.īalanced output where cold lead is actively driven by inverted signal This is a conventional single-ended connection and it is unbalanced as the hot lead has 1 Ω impedance to ground but the cold lead has 0 Ω impedance to ground. Return path is ground-referenced and in practice the shield in the cable (if there is one) acts as a shield and return signal path. Let us assume the amplifier has 0 Ω output impedance and the 1 Ω resistor represents the output impedance. Unbalanced (single-ended) exampleīelow is an illustration of a conventional single-ended connection to a headphone speaker in a line-level example there could be an input stage instead of a speaker.
Signal is differential, as is the following input stage. Moreover, inductance and capacitance must be taken into account as well, not only resistance.Īlthough my wording is not exact and perfectly consistent either, I would like to say that a system or interconnection is balanced, not signal. Regarding balance, the whole chain of output, cable, and input are of interest. However, the main advantages come from the impedance balance between the two conductors. It does not mean that two signals of opposite phase are driven although this is often the case and can have additional benefits. The most important thing to understand is that the word balanced in interconnection refers to impedance balance the two signal conductors have equal impedance to ground (or some other reference). Balanced interconnection always means two conductors are involved in signal transfer but there is often confusion and misinformation regarding the meaning of balance. unbalanced headphones interconnectionīalanced interconnection is a common concept in electronics and used in numerous applications from very sensitive analog signals to high-speed digital buses. Line-level balanced interconnections are not discussed here in detail but as it is a well documented topic, references are provided. Crosstalk measurements are also provided comparing unbalanced and balanced connection. The main focus is on the reduced common-impedance coupling which is more significant benefit in balanced headphones than noise suppression which is often considered the main reason for going balanced. Here is a brief introduction to balanced interconnection and its benefits. Balanced output can be easily and cost-effectively added on designs inverted signal is not required.Common-impedance coupling seriously limits crosstalk in conventional unbalanced headphones.Crosstalk can be improved by tens of dB by using balanced interconnection.
In balanced connection both speakers are individually connected to amplifier using two wires for each channel.
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